This invention relates to the structure of a drum for a brake band for stopping the rotation of one member of a planetary gear in a planetary gear-type transmission.
FIGS. 4(a) and 4(b) illustrate the structure of a direct clutch and second coast brake in a conventional planetary gear-type transmission, in which FIG. 4(a) is a sectional view and FIG. 4(b) a perspective view of a clutch cylinder.
A planetary gear mechanism 3 is arranged about an intermediate shaft 2 coupled to an input shaft 1 for engine power. The planetary gear mechanism 3 includes a sun gear S fitted onto the outer periphery of the intermediate shaft 2, a ring gear R, and a carrier C supporting a pinion P meshing with these gears. The carrier CR is fitted on the outer periphery of the intermediate shaft 2.
The ring gear R is connected to a clutch cylinder 5 fitted on the input shaft 1, and the ring gear R and clutch cylinder 5 are engaged and disengaged by a piston 6. The clutch cylinder 5 is connected to a clutch cylinder 8 via a clutch 7, and the two clutches 5, 8 are engaged and disengaged by a piston 9. A band drum 10 is fixed to the outer periphery of the clutch cylinder 8 by electron beam welding. The band drum 10 is splined to a sun gear input drum 11 and secured to the sun gear S. By operating a band brake 12 arranged on the outer periphery of the band drum 10, stopping of the band drum 10 is controlled to halt rotation of the sun gear S.
As shown in (b) of FIG. 4, the clutch cylinder 8 is formed to include recesses 13 and protuberances 14 by pressing work. A clutch frictional engagement plate 15 is splined in each protuberance 14. Therefore, when the band brake 12 is tighened on the recesses 13 and protuberances 14, the band is damaged. Consequently, the band drum 10 is fixed to the outer periphery of the clutch cylinder 8 by electron beam welding and the band brake 12 is tightened along the flat outer periphery of the band drum 10.
However, in the above-described conventional structure of the brake band drum, welding means as for electron beam welding are required in order to fix the band drum 10 on the outer periphery of the clutch cylinder 8. A problem that arises as a result is higher cost. In addition, since welding distortion is brought about by the welding operation, another problem is that the piston sliding surface of the clutch cylinder 8 on the inner peripheral side must be machined after welding. A further drawback is that the surface of the welded joint is required to be finished and press-fitted in advance by machining.
Moreover, since the band drum 10 is large in diameter and generally comprises a drum made of steel, the drum is very heavy. Such a drum offers problems in terms of being installed in a light-weight automotive vehicle. Owing to the great weight of the band drum, the load-bearing capacity of the bearings arranged on the inner periphery of the clutch cylinder 8 is high, thereby resulting in reduced bearing durability.